Planetside has a persistant battlefield stretched across several different continents. If an empire takes control of a continent, it will remain under their control until another empire lands troops there to take over bases. It has leveling up for players (as in, when you level up you get 1 point to spend on unlocking a vehicle/weapon/support ability, which can be changed every 6 hours).
I really dont care, but a game doesn't need to be ANYTHING like that to be a MMO
(massively multiplayer online game). If the bolded tells you nothing, I have no reason to try and explain that Gunz, Crossfire, Combat Arms, and so on can be a MMO
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Have a list:
http://www.massivefps.com/Game-List/I see some games he listed on this list.